Charles Ellicott Commentary Isaiah 26:1

"In that day shall this song be sung in the land of Judah: we have a strong city; salvation will he appoint for walls and bulwarks." — Isaiah 26:1 (ASV)

In that day shall this song be sung ... —The prophet appears once more, as in Isaiah 5:1; Isaiah 12:4, in the character of a psalmist, and what he writes is destined for nothing less than the worship of the new city of the heavenly kingdom.

Salvation will God appoint for walls. —Better, salvation He appoints. The walls of the heavenly city are not of stone or brick, but are themselves as a living force, saving and protecting. The same characteristic thought appears in Isaiah 60:18.